1. Field of the Invention
The present invention relates generally to a brake apply system in a vehicle driven by a cross-drive transmission. In particular, the present invention is concerned with a self-adjustment mechanism provided between a brake apply cam and a brake apply piston, and a method for adjusting the linkage between the brake apply cam and the brake apply piston.
2. Description of the Related Art
Cross-drive transmissions for track-laying vehicles customarily provide an arrangement for decelerating the vehicle by dissipating a portion or all of the vehicle's kinetic energy in brakepacks comprised of multiple friction and reaction disc plates at each output shaft. When a brakepack is compressed during application of the brakes, a decelerating torque is applied to each output shaft. The brakepacks are compressed by axially-stroking apply pistons that are both hydraulically and mechanically applied for some applications. A predetermined range of axial brakepack running clearance must be maintained when the brakes are unapplied to minimize both brake apply time and friction horsepower loss through the brakes. A mechanical adjustment mechanism is normally applied in the brake apply piston linkage to allow maintenance of the axial clearance, compensating for both dimensional manufacturing variations in brake components and frictional wear of brake plate materials.
In certain applications, the service brakes and the emergency/parking brake must be applied through the same pedal. This requirement often complicates the linkage design due to the conflicting ergonomic constraints of maintaining low pedal stroke for the service brake pedal while attaining an adequate combination of pedal stroke and force to take up brakeplate running clearance and provide specified mechanical braking torque. These conflicting requirements can be accommodated through the use of a variable mechanical advantage cam in the brake linkage. Such a cam provides low mechanical advantage when taking up brakeplate running clearance while delivering high mechanical advantage where it is required as the brakepack is clamped. Only a small fraction of the brake pedal stroke is used to take up the running clearance, while most of the stroke is retained for providing the high mechanical advantage during brakepack clamp engagement.
A potential drawback with a cam-based system is that small amounts of brake plate wear translate into significant increases in brake pedal stroke. To avoid this brake pedal stroke increase, frequent brake adjustments are required. Also, the use of brake friction material that resists wear and the use of a brake adjustment mechanism have been utilized in conventional brake systems to overcome pedal stroke increase.